The impending ban on incandescent light bulbs has found many vocal opponents, including those who says CFL or LED bulbs just cant match the warm glow of an old-fashioned incandescent. We tested all three to find out if theyre right.

The color temperature of a light, measured in kelvins, is its most noticeable characteristic. A candle, at 1900 K, appears orange. Daylight, at 5500 K, is much whiter and bluer. A 5500-K bulb, however, will not necessarily produce the same light as the sun; for the full nature of a light source, one must look to its spectral power distribution (SPD) curve, which describes its irradiance across the entire visible spectrum. An incandescent bulb achieves its temperature by emitting light over a smooth curve, with the balance tilted toward yellow and red. A CFL, and to a lesser extent an LED, mimics incandescents using a different mixture of light, with spikes and troughs of power strategically positioned across the spectrum to create a correlated—or averaged—color temperature. This results in less faithful reproduction of colors, expressed as a diminished color rendering index (CRI).
How We Tested
Readings for color temperature, color rendering and spectral distribution were taken with an Ocean Optics USB2000 Miniature Fiber Optic Spectrometer, provided and calibrated by SpectrEcology of Jasper, Ga. Subjective testing was performed by volunteers in PM's test lab who observed bulbs hidden behind a white shade.

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Typozon

Decoding the Science of Light

The color temperature of a light, measured in kelvins, is its most noticeable characteristic. A candle, at 1900 K, appears orange. Daylight, at 5500 K, is much whiter and bluer. A 5500-K bulb, however, will not necessarily produce the same light as the sun; for the full nature of a light source, one must look to its spectral power distribution (SPD) curve, which describes its irradiance across the entire visible spectrum. An incandescent bulb achieves its temperature by emitting light over a smooth curve, with the balance tilted toward yellow and red. A CFL, and to a lesser extent an LED, mimics incandescents using a different mixture of light, with spikes and troughs of power strategically positioned across the spectrum to create a correlated—or averaged—color temperature. This results in less faithful reproduction of colors, expressed as a diminished color rendering index (CRI).

How We Tested

Readings for color temperature, color rendering and spectral distribution were taken with an Ocean Optics USB2000 Miniature Fiber Optic Spectrometer, provided and calibrated by SpectrEcology of Jasper, Ga. Subjective testing was performed by volunteers in PM's test lab who observed bulbs hidden behind a white shade.

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programwitch/Flickr

Incandescent Bulbs

An incandescent bulb emits light by heating a tungsten filament surrounded by various inert gases to about 4000 F. These bulbs light well and cost little, but die quickly and are highly inefficient, releasing 90 percent of their energy as heat. In incandescent bulbs, PM's testers noted yellow hues and warm light.

Inside a CFL, an electric current is driven through a tube filled with argon and a small amount of mercury vapor. This creates invisible UV light, which excites a phosphor coating that reacts by emitting visible light. CFLs are efficient and long-lasting, but take time to warm up. With CFLs, PM's testers noted inconsistent light qualities.

LEDs are composed of two conjoined sections of a semiconductor material. When an LED is energized, movement of electrons across the diode causes emission of photons—or light. LED lamps are efficient, produce little heat and have extremely long life spans, but are costly. In LEDs, PM's testers noted pleasing light but a lack of power.

INCANDESCENT: Operating at several thousand degrees Fahrenheit, the tungsten filament—up to 6.5 feet long—evaporates over time. Eventually, it breaks apart because of wear or uneven heat distribution—often popping in a "burnout arc."

CFL: In most cases, the emissive coating on the bulb's cathodes is diminished, or sputtered off, and the bulb simply goes out. If the bulb's ballast fails first, its electronics can overheat, causing audible crackles and sometimes melting the bulb's plastic base. It may appear dangerous, but don't worry—CFLs are designed to fail this way.

LED: Over time, the semiconductor materials lose their capacity to transfer electrons, resulting in a gradual loss of brightness.

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Philip Friedman

Rolling Blackout

The lighting-efficiency requirements of the Energy Independence and Security Act of 2007 will start requiring consumers to switch from traditional incandescent bulbs on Jan. 1, 2012. So which bulbs get phased out, and when?

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